Mixed-grade plastics from communal and/or industrial wastes cause considerable difficulties as regards possible reclamation because of the mixture of grades, on the one hand, and, on the other hand, because of the necessity of washing to remove impurities, especially since, even after washing, residues of impurities such as sand, foil fragments not made of plastic, wood pieces and the like, together with a corresponding residual moisture content are present.
Although it is known to compression mould flower pots, fence posts and the like from such plastic wastes under the effect of heat, these products are relatively inferior in quality, on the one hand, and, on the other hand, this does not result in an important product, but essentially only waste disposal, which otherwise does not lead to the processing of large amounts of wastes.
Nor are any of the pelletizing processes which are conventional in the plastics industry and used for pure-grade plastics suitable to allow large amounts of such plastic wastes, or even pure-grade plastic wastes, to be processed to form intermediate products which can be used forever. For example, a production of coarse-grained intermediate products, for example by means of a heated extruder, would be, because of the low power attainable, firstly uneconomical and secondly unsuitable with respect to the amounts produced. Difficulties are caused here by, inter alia, the poor thermal conductivity of the plastic wastes which impair the heating and cooling.